The effects of a brief course of leukapheresis were studied in eleven patients with Rheumatoid Arthritis, unresponsive to conventional therapy. The patients consisted of two groups--those with profoundly depressed or normal proliferation to soluble antigens. They represented the extremes of our rheumatoid patient population. Six of 7 patients with depressed proliferation clinically improved, whereas 0/4 patients with normal proliferation clincally improved. This and other immunologic abnormalities tended to normalize in the group which clinically improved. Thus, reversal of depressed immune function appeared to parallel clinical improvement. These studies provide new insights into the pathogenesis of rheumatoid arthritis and more insight ito the effects of leukapheresis.